Photoproduction of Pion Pairs in Hydrogen

The photoproduction of pion pairs (${\pi }^{-}+{\pi }^{+}$) has been measured by observing a ${\pi }^{-}$ signal from liquid hydrogen bombarded with bremsstrahlung of energies up to 600 Mev. The excitation function and ${\pi }^{-}$ energy spectrum measured at 60° in the laboratory system agree qualitatively with the calculations of Cutkowsky and Zachariasen. The major part of the process corresponds to the emission of the ${\pi }^{+}$ in the resonant $P$ state and the ${\pi }^{-}$ in an $S$ state. The net increase in the ${\pi }^{+}$ yield due to (${\pi }^{-}+{\pi }^{+}$) and (${\pi }^0+{\pi }^{+}$) pairs is also observed.